1. Field of the Invention
The present invention relates to an ink-droplet jetting apparatus of an ink-jet type.
2. Description of the Related Art
As a head provided to an ink-jet printer which is an ink-droplet jetting apparatus, an ink-jet head which jets an ink droplet from a nozzle by changing a volume of a pressure chamber in which the ink is filled, by displacing an electromechanical transducer such as a piezoelectric element by applying a drive pulse signal has hitherto been known.
In the abovementioned ink-jet head, a gradation control (a half-toning control) in which, a dot diameter is changed is carried out. For forming one dot by a plurality of ink droplets, the drive pulse signal is set such that a plurality of pulses is applied continuously. For suppressing an effect on a subsequent jetting of vibration which is left in the ink after the ink droplets are jetted (residual vibration), a regulating pulse (canceling pulse) is output after a main pulse which jets the ink. For example, U.S. Pat. No. 6,412,923 (corresponds to Japanese Patent Application Laid-open No. 2001-52561) discloses that, a plurality of pulse sets are output one after another, and the ink-jet head is driven at a frequency of 8.5 kHz by these pulse sets for forming one dot, each of the pulse sets including a first-droplet jetting pulse, a regulating pulse, a second-droplet jetting pulse, and a regulating pulse.